Aerogel composite powder

ABSTRACT

The present invention relates to an aerogel composite powder superior in thermal insulation and flexibility, the aerogel composite powder comprising an aerogel component and a silica particle.

TECHNICAL FIELD

The present disclosure relates to an aerogel composite powder.

BACKGROUND ART

Silica aerogels are known as materials having thermal insulation with low thermal conductivity. Silica aerogels are useful as functional raw materials with superior functionality (e.g., thermal insulation), unique optical properties, unique electric properties, etc., and used for, for example, materials for electronic substrates, which utilize the property of an ultralow dielectric constant of a silica aerogel, thermal insulation materials, which utilize the high thermal insulation of a silica aerogel, and light reflective materials, which utilize the ultralow refractive index of a silica aerogel.

Supercritical drying is known as a method for producing such a silica aerogel, in which a gel compound (alcogel) obtained by hydrolyzing and polymerizing an alkoxysilane is dried under supercritical conditions for a dispersion medium (e.g., see Patent Literature 1). Supercritical drying is a method in which an alcogel and a dispersion medium (a solvent used for drying) are introduced into a high-pressure container, and a temperature and pressure equal to or higher than the critical point of the dispersion medium is applied to the dispersion medium to convert it into a supercritical fluid, thereby removing the solvent contained in the alcogel. However, supercritical drying requires a high-pressure process, and hence needs capital investment for special apparatuses or the like capable of enduring supercritical condition, as well as much time and effort.

In view of this, techniques of drying an alcogel with a versatile method without need of any high-pressure process have been proposed. A known example of such a method is a method in which monoalkyltrialkoxysilane and tetraalkoxysilane are used in combination with a specific ratio as gel materials to enhance the strength of the resulting alcogel, and the alcogel is dried under ambient pressure (e.g., see Patent Literature 2). When such ambient pressure drying is employed, however, the gel tends to shrink because of a stress caused by capillary force in the inside of the alcogel.

CITATION LIST Patent Literature

Patent Literature 1: U.S. Pat. No. 4,402,927

Patent Literature 2: Japanese Unexamined Patent Publication No. 2011-93744

SUMMARY OF INVENTION Technical Problem

Although attempts have been made from various viewpoints to overcome problems inherent in conventional production processes as described above, aerogels produced with any of the processes have low mechanical strength, and hence have disadvantages such as brittleness. For example, an aerogel obtained with any of the processes may be broken only on undergoing stress such as compression. The reason is probably that the density of the aerogel is low and that the aerogel has a porous structure in which fine particles with a size of around 10 nm are only weakly linked together. An aerogel powder obtained by powdering such a brittle aerogel also has low mechanical strength, and the pore structure of the powder may be broken by stress applied in a process of mixing or kneading with resin.

The present disclosure was made in consideration of the above-described circumstances, and an object of the present disclosure is to provide an aerogel composite powder superior in thermal insulation and flexibility.

Solution to Problem

The present inventors diligently studied to achieve the object, and found that superior thermal insulation and superior flexibility are exhibited when a composite of a silica particle is formed in an aerogel.

The present disclosure provides an aerogel composite powder comprising an aerogel component and a silica particle. In contrast to aerogel powders obtained by using any of conventional techniques, the aerogel composite powder according to the present disclosure is superior in thermal insulation and flexibility.

The aerogel composite powder can have: a three-dimensional network skeleton formed of the aerogel component and the silica particle; and a pore. Thereby, it becomes easier to further improve thermal insulation and flexibility.

The present disclosure provides an aerogel composite powder comprising a silica particle as a component constituting a three-dimensional network skeleton. The aerogel composite powder obtained in this manner is superior in thermal insulation and flexibility.

The present disclosure provides an aerogel composite powder as a dried product of a wet gel, wherein the wet gel is a condensate of a sol comprising: a silica particle; and at least one selected from the group consisting of a silicon compound having a hydrolyzable functional group or a condensable functional group and a hydrolysis product of the silicon compound having a hydrolyzable functional group. The aerogel composite obtained in this manner is superior in thermal insulation and flexibility.

The above-described aerogel composite powders may be each a dried product of a wet gel, wherein the wet gel is a condensate of a sol comprising: a silica particle; and at least one selected from the group consisting of a silicon compound having a hydrolyzable functional group or a condensable functional group and a hydrolysis product of the silicon compound having a hydrolyzable functional group.

In the present disclosure, the silicon compound can further comprise a polysiloxane compound having a hydrolysable functional group or a condensable functional group. Thereby, more superior thermal insulation and more superior flexibility can be achieved.

The polysiloxane compound can include a compound having a structure represented by the following formula (B):

wherein R^(1b) represents an alkyl group, an alkoxy group, or an aryl group; R^(2b) and R^(3b) each independently represent an alkoxy group; R^(4b) and R^(5b) each independently represent an alkyl group or an aryl group; and m represents an integer of 1 to 50.

The aerogel composite can be in a mode having a ladder-type structure including struts and a bridge, wherein the bridge has a structure represented by the following formula (2):

wherein R⁵ and R⁶ each independently represent an alkyl group or an aryl group; and b represents an integer of 1 to 50.

The aerogel composite can have a ladder-type structure represented by the following formula (3):

wherein R⁵, R⁶, R⁷, and R⁸ each independently represent an alkyl group or an aryl group; a and c each independently represent an integer of 1 to 3000; and b represents an integer of 1 to 50.

The average primary particle diameter of the silica particle can be 1 to 500 nm. Thereby, it becomes easier to further improve thermal insulation and flexibility.

In this case, the shape of the silica particle can be spherical. The silica particle can be an amorphous silica particle, and the amorphous silica particle can be at least one selected from the group consisting of a fused silica particle, a fumed silica particle, and a colloidal silica particle. Thereby, more superior thermal insulation and more superior flexibility can be achieved.

In the present disclosure, the average particle diameter D50 of the aerogel composite powder can be 1 to 1000 μm. Thereby, good dispersibility and good handleability can be achieved.

Advantageous Effects of Invention

The present disclosure can provide an aerogel composite powder superior in thermal insulation and flexibility. Specifically, the present disclosure can provide an aerogel composite powder which exhibits superior thermal insulation and is flexible and less likely to be broken even on undergoing stress such as compression. The aerogel composite powder, which is superior in thermal insulation and flexibility as described above, has potential utility for a wide variety of applications. Here, an important point of the present disclosure is that the thermal insulation and flexibility can be controlled more easily than those of conventional aerogel powders. This is a matter which conventional aerogel powders have not achieved, because conventional aerogel powders need to sacrifice the thermal insulation for flexibility or to sacrifice the flexibility for thermal insulation. The phrase “superior in thermal insulation and flexibility” does not necessarily mean that numerical values as indicators of the two properties are both large, and encompasses, for example, “superior in flexibility with the thermal insulation satisfactorily maintained” and “superior in thermal insulation with the flexibility satisfactorily maintained”.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a diagram schematically illustrating the microstructure of an aerogel composite according to an embodiment of the present invention.

FIG. 2 shows a diagram for description of a method for calculating the biaxial average primary particle diameter of a particle.

DESCRIPTION OF EMBODIMENTS

Hereinafter, preferred embodiments of the present disclosure will be described in detail occasionally with reference to the drawings. However, the present disclosure is not limited to the embodiments below. In the present specification, a numerical range expressed with “to” represents a range including the numerical values set forth before and after “to” as the minimum value and the maximum value, respectively. When the phrase “A or B” is used, it is only required to include one of A and B, and both of A and B may be included. With respect to materials exemplified in the present embodiments, one material may be used singly, or two or more materials may be used in combination, unless otherwise stated.

<Aerogel Composite Powder>

In a narrow sense, dry gel obtained by using supercritical drying for wet gel is referred to as aerogel, dry gel obtained by drying under the atmospheric pressure is referred to as xerogel, and dry gel obtained by using freeze drying is referred to as cryogel; however, a dry gel with low density obtained by using any of these techniques for drying wet gel is referred to as “aerogel” in the present embodiments. That is, the term “aerogel” in the present embodiments means aerogel in a broad sense, namely, “Gel comprised of a microporous solid in which the dispersed phase is a gas”. In general, the inside of aerogel is formed of a fine network structure, and has a cluster structure in which aerogel particles (particles constituting the aerogel) with a size of around 2 to 20 nm are bonded together. Among skeletons formed in the cluster, pores with a size smaller than 100 nm are present. For this reason, aerogel has a three-dimensional fine porous structure. Aerogel in the present embodiments is, for example, silica aerogel, which comprises silica as a primary component. Examples of the silica aerogel include silica aerogel with an organic group (e.g., a methyl group) or an organic chain introduced therein, what is called organic-inorganic-hybridized silica aerogel. The aerogel composite powder (also expressed as the powdery aerogel composite) in the present embodiments includes a composite of a silica particle in an aerogel, and at the same time has a cluster structure, which is a feature of the aerogel, and thus is a powder having a three-dimensional fine porous structure.

The aerogel composite powder in the present embodiments comprises an aerogel component and a silica particle. In another possible expression, although the expression does not necessarily have the same meaning as the previously-mentioned concept, the aerogel composite powder in the present embodiments comprises a silica particle as a component constituting a three-dimensional network skeleton. The aerogel composite powder in the present embodiments is superior in thermal insulation and flexibility as described later. In particular, the superior flexibility results in provision of an aerogel composite powder which is flexible and less likely to be broken even on undergoing stress such as compression. Such an aerogel composite powder is obtained by allowing a silica particle to be present in the environment of aerogel production. The advantage by allowing a silica particle to be present is not only that the thermal insulation, flexibility, and so on of the aerogel composite powder itself can be improved, but also that reduction of time for a step of forming wet gel, which is described later, and simplification of steps from a step of washing and solvent displacement to a step of drying can be achieved. It should be noted that the reduction of time for the step and the simplification of the steps are not necessarily required in production of an aerogel composite powder superior in flexibility.

In the present embodiments, various modes for the composite of the aerogel component and the silica particle are contemplated. For example, the aerogel component may be in an irregular shape such as a film, or be particulate (aerogel particle). In any mode, the aerogel component in various forms is present in between the silica particles, which is inferred to impart flexibility to the skeleton of the composite.

Examples of modes for the composite of the aerogel component and the silica particle include a mode in which the aerogel component in an irregular shape exists between the silica particles. Specific examples of such a mode include various modes including: a mode in which the silica particle is covered by a film of the aerogel component (silicone component) (a mode in which the aerogel component includes the silica particle therein); a mode in which the silica particles are bonded with each other via the aerogel component as a binder; a mode in which the aerogel component fills a plurality of voids of the silica particle; and a mode of combination of these modes (e.g., a mode in which a cluster array of the silica particle is covered by the aerogel component). As just described, the three-dimensional network skeleton of the aerogel composite powder in the present embodiments can be constituted with the silica particle and the aerogel component (silicone component), and the specific mode (embodiment) thereof is not limited in any way.

On the other hand, the aerogel component in the present embodiments may form a definite particulate composite, not in an irregular shape, with the silica particle as illustrated in FIG. 1 as described later.

Although the mechanism of formation of such various modes in the aerogel composite powder in the present embodiments is not necessarily clear, the present inventor suspects the formation rate of the aerogel component in a step of gelling to be involved therein. For example, the formation rate of the aerogel component tends to vary as the number of silanol groups of the silica particle varies. In addition, the formation rate of the aerogel component tends to vary as the pH of the system varies.

These suggest that the mode of the aerogel composite powder (e.g., the size and the shape of the three-dimensional network skeleton) can be controlled through adjustment of the size, shape, and number of silanol groups of the silica particle, and the pH and so on of the system. Accordingly, the density, porosity, and so on of the aerogel composite can be controlled, and hence the thermal insulation and flexibility of the aerogel composite can be controlled. The three-dimensional network skeleton of the aerogel composite powder may be constituted with only one of the above-described various modes, or with two or more of the modes.

Now, the aerogel composite powder in the present embodiments will be described with reference to FIG. 1 as an example, though the present disclosure is not limited to the mode in FIG. 1 as described above. However, the following description can be appropriately referred to with regard to matters common among the above modes (e.g., the type, size, content of the silica particle).

FIG. 1 shows a diagram schematically illustrating the microstructure of an aerogel composite powder according to an embodiment of the present disclosure. As illustrated in FIG. 1, an aerogel composite 10 has: a three-dimensional network skeleton formed of three-dimensional random linkage of an aerogel particle 1 constituting the aerogel component with a silica particle 2 partially intervening; and a pore 3 surrounded by the skeleton. In this case, the silica particles 2 are present in between the aerogel particles 1, and inferred to function as a skeleton support to support the three-dimensional network skeleton. Hence, this structure probably imparts moderate strength to aerogel while thermal insulation and flexibility as aerogel are maintained. It follows that the aerogel composite powder in the present embodiments may have a three-dimensional network skeleton formed of three-dimensional random linkage of a silica particle with an aerogel particle intervening. The silica particle may be covered by the aerogel particle. The aerogel particle (aerogel component) is constituted with a silicon compound, and hence inferred to have high affinity to the silica particle. Probably for this reason, the silica particle was successfully introduced into the three-dimensional network skeleton of aerogel in the present embodiments. In this regard, silanol groups of the silica particle probably contribute to the affinity between the aerogel particle and the silica particle.

The aerogel particle 1 is inferred to be in a mode of a secondary particle constituted with a plurality of primary particles, and generally spherical. The average particle diameter (i.e., secondary particle diameter) of the aerogel particle 1 can be 2 nm or larger, and may be 5 nm or larger or 10 nm or larger. The average particle diameter can be 50 μm or smaller, and may be 2 μm or smaller or 200 nm or smaller. In other words, the average particle diameter can be 2 nm to 50 μm, and may be 5 nm to 2 μm or 10 nm to 200 nm. It becomes easier to obtain an aerogel composite powder superior in flexibility by setting the average particle diameter of the aerogel particle 1 to 2 nm or larger, and, on the other hand, it becomes easier to obtain an aerogel composite powder superior in thermal insulation by setting the average particle diameter to 50 μm or smaller. The average particle diameter of the primary particle constituting the aerogel particle 1 can be 0.1 nm to 5 μm because of easiness in forming a secondary particle with a porous structure of low density, and may be 0.5 nm to 200 nm or 1 nm to 20 nm.

Any silica particle can be used for the silica particle 2 without any limitation, and examples thereof include an amorphous silica particle. Examples of the amorphous silica particle include at least one selected from the group consisting of a fused silica particle, a fumed silica particle, and a colloidal silica particle. Among them, the colloidal silica particle has high monodispersity and facilitates prevention of aggregation in a sol. The silica particle 2 may be a silica particle having a hollow structure, a porous structure, or the like.

The shape of the silica particle 2 is not limited in any way, and examples thereof include a sphere, a cocoon, and an association. Use of the spherical particle among them as the silica particle 2 facilitates prevention of aggregation in a sol. The average primary particle diameter of the silica particle 2 can be 1 nm or larger, and may be 5 nm or larger or 20 nm or larger. The average primary particle diameter can be 500 nm or smaller, and may be 300 nm or smaller or 100 nm or smaller. In other words, the average primary particle diameter can be 1 to 500 nm, and may be 5 to 300 nm or 20 to 100 nm. By setting the average primary particle diameter of the silica particle 2 to 1 nm or larger, it becomes easier to impart moderate strength to aerogel and obtain an aerogel composite powder superior in shrinkage resistance in drying. By setting the average primary particle diameter to 500 nm or smaller, on the other hand, it becomes easier to suppress the solid thermal conduction of the silica particle and obtain an aerogel composite powder superior in thermal insulation.

The aerogel particle 1 (aerogel component) and the silica particle 2 are inferred to be bonding together in a mode of hydrogen bonding or chemical bonding. In this situation, the hydrogen bonding or chemical bonding is probably formed of a silanol group or reactive group of the aerogel particle 1 (aerogel component) and a silanol group of the silica particle 2. Therefore, it probably becomes easier to impart moderate strength to aerogel if the mode of bonding is chemical bonding. In view of this, the particle to form a composite with the aerogel component is not limited to the silica particle, and an inorganic particle or organic particle having a silanol group on the particle surface can be also used.

The number of silanol groups of the silica particle 2 per 1 g can be 10×10¹⁸ to 1000×10¹⁸ groups/g, and may be 50×10¹⁸ to 800×10¹⁸ groups/g or 100×10¹⁸ to 700×10¹⁸ groups/g. By setting the number of silanol groups of the silica particle 2 per 1 g to 10×10¹⁸ groups/g or more, the silica particle 2 can have better reactivity with the aerogel particle 1 (aerogel component), and it becomes easier to obtain an aerogel composite powder superior in shrinkage resistance. By setting the number of silanol groups of the silica particle 2 per 1 g to 1000×10¹⁸ groups/g or less, it becomes easier to prevent rapid gelling in production of a sol and obtain a homogeneous aerogel composite powder.

In the present embodiments, the average particle diameter of a particle (e.g., the average secondary particle diameter of the aerogel particle, the average primary particle diameter of the silica particle) can be determined through direct observation of a cross-section of the aerogel composite by using a scanning electron microscope (hereinafter, abbreviated as “SEM”). For example, individual particle diameters can be determined for the aerogel particle or the silica particle on the basis of the diameter of the cross-section of the three-dimensional network skeleton. The diameter here refers to a diameter when the cross-section of a skeleton forming the three-dimensional network skeleton is regarded as a circle. The diameter when the cross-section is regarded as a circle refers to a diameter of a circle with an area equal to that of the cross-section. In calculation of an average particle diameter, the diameter of a circle is determined for 100 particles, and the diameters are averaged.

The average particle diameter of the silica particle can be determined from measurement for the raw material. For example, the biaxial average primary particle diameter can be calculated from results of observation of arbitrarily selected 20 particles by using SEM as follows. Taking a colloidal silica particle with a solid concentration of 5 to 40% by mass, which is typically dispersed in water, as an example, a 2 cm×2 cm chip cut out of a wafer with a wiring pattern is soaked in a dispersion of the colloidal silica particle for approximately 30 seconds, and the chip is then rinsed with pure water for approximately 30 seconds and dried with nitrogen blowing. Thereafter, the chip is set on a sample stage for SEM observation, and an accelerating voltage of 10 kV is applied, and the silica particle is observed at a magnification of 100000× to take an image. From the image taken, 20 silica particles are arbitrarily selected, and the mean of the particle diameters of the particles is used as the average particle diameter. Here, when a silica particle selected has a shape illustrated in FIG. 2, a rectangle positioned in a manner such that the rectangle is circumscribed about the silica particle 2 and the long side is maximized (circumscribed rectangle L) is derived. The long side and short side of the circumscribed rectangle L are defined as X and Y, respectively, and the biaxial average primary particle diameter is calculated as (X+Y)/2, which is used as the particle diameter of the particle.

The size of the pore 3 in the aerogel composite powder will be described in the section [Density and porosity] described later.

The content of the aerogel component comprised in the aerogel composite powder can be 4 parts by mass or more, and may be 10 parts by mass or more, with respect to 100 parts by mass of the total amount of the aerogel composite powder. The content can be 25 parts by mass or less, and may be 20 parts by mass or less. In other words, the content can be 4 to 25 parts by mass, and may be 10 to 20 parts by mass. It becomes easier to impart moderate strength by setting the content to 4 parts by mass or more, and it becomes easier to obtain better thermal insulation by setting the content to 25 parts by mass or less.

The content of the silica particle comprised in the aerogel composite powder can be 1 part by mass or more, and may be 3 parts by mass or more, with respect to 100 parts by mass of the total amount of the aerogel composite powder. The content can be 25 parts by mass or less, and may be 15 parts by mass or less. In other words, the content can be 1 to 25 parts by mass, and may be 3 to 15 parts by mass. It becomes easier to impart moderate strength to the aerogel composite by setting the content to 1 part by mass or more, and it becomes easier to suppress the solid thermal conduction of the silica particle by setting the content to 25 parts by mass or less.

For the purpose of suppressing radiation of heat rays, the aerogel composite powder may further comprise an additional component such as carbon graphite, an aluminum compound, a magnesium compound, a silver compound, and a titanium compound, in addition to the aerogel component and the silica particle. The content of the additional component is not limited in any way, and can be 1 to 5 parts by mass with respect to 100 parts by mass of the total amount of the aerogel composite powder to sufficiently ensure desired effects of the aerogel composite.

[Thermal Conductivity]

Because it is difficult to measure the thermal conductivity of a powder, the thermal conductivity of the aerogel composite powder in the present embodiments is determined through measurement of the thermal conductivity of an aerogel composite block before crushing, which is described later. The thermal conductivity under the atmospheric pressure at 25° C. can be 0.03 W/(m·K) or lower, and may be 0.025 W/(m·K) or lower or 0.02 W/(m·K) or lower. Thermal insulation equal to or higher than that of polyurethane foam, a high-performance heat insulator, can be obtained by setting the thermal conductivity to 0.03 W/m·K or lower. The lower limit of the thermal conductivity is not limited in any way, and can be, for example, 0.01 W/m·K.

The thermal conductivity can be measured in accordance with a steady state method. Specifically, the thermal conductivity can be measured, for example, by using the thermal conductivity analyzer based on a steady state method “HFM 436 Lambda” (produced by NETZSCH, product name, HFM 436 Lambda is a registered trademark). Summary of a method for measuring the thermal conductivity by using the thermal conductivity analyzer based on a steady state method is as follows.

(Preparation of Measurement Sample)

The aerogel composite block is processed into a piece in a size of 150×150×100 mm³ by using a blade with a blade angle of approximately 20 to 25 degrees, and the piece is used as a measurement sample. Here, the thermal conductivity measured with the sample size has been already confirmed to be almost the same as the thermal conductivity measured with the recommended sample size for the HFM 436 Lambda, 300×300×100 mm³. Subsequently, the measurement sample is shaped with a sand paper of #1500 or finer to thoroughly smooth the surface, as necessary. Before measurement of thermal conductivity, the measurement sample is dried by using the thermostatic dryer “DVS402” (produced by Yamato Scientific Co., Ltd., product name) under the atmospheric pressure at 100° C. for 30 minutes. The measurement sample is then transferred into a desiccator and cooled to 25° C. Thus, a measurement sample for measurement of the thermal conductivity is obtained.

(Measurement Method)

Measurement conditions are set such that measurement is performed under the atmospheric pressure at an average temperature of 25° C. The measurement sample obtained as described above is sandwiched between an upper heater and a lower heater with a load of 0.3 MPa, the temperature difference, ΔT, is set to 20° C., and the upper surface temperature, lower surface temperature, and so on of the measurement sample are measured while the heat flow is adjusted to a one-dimensional heat flow by using a guard heater. The thermal resistance, R_(S), of the measurement sample is determined by using the following equation:

R _(S) =N((T _(U) −T _(L))/Q)−R _(O)

wherein T_(U) denotes the upper surface temperature of the measurement sample; T_(L) denotes the lower surface temperature of the measurement sample; R_(O) denotes the contact thermal resistance of the upper/lower interface; and Q denotes output from a heat flux meter. N denotes a proportionality coefficient, and is determined in advance by using a calibration sample.

From the thermal resistance, R_(S), obtained, the thermal conductivity, λ, of the measurement sample is determined by using the following equation:

λ=d/R _(S)

wherein d denotes the thickness of the measurement sample.

[Compression Modulus]

Because it is difficult to measure the compression modulus of a powder, the compression modulus of the aerogel composite powder in the present embodiments is determined through measurement of the compression modulus of an aerogel composite block before crushing, which is described later. The compression modulus at 25° C. can be 3 MPa or lower, and may be 2 MPa or lower or 1 MPa or lower or 0.5 MPa or lower. It becomes easier to obtain an aerogel composite powder superior in handleability by setting the compression modulus to 3 MPa or lower. The lower limit of the compression modulus is not limited in any way, and can be, for example, 0.05 MPa.

[Deformation Recovery Rate]

Because it is difficult to measure the deformation recovery rate of a powder, the deformation recovery rate of the aerogel composite powder in the present embodiments is determined through measurement of the deformation recovery rate of an aerogel composite block before crushing, which is described later. The deformation recovery rate at 25° C. can be 90% or higher, and may be 94% or higher or 98% or higher. It becomes easier to obtain superior strength, superior flexibility against deformation, and the like by setting the deformation recovery rate to 90% or higher. The upper limit of the deformation recovery rate is not limited in any way, and can be, for example, 100% or 99%.

[Maximum Compression Deformation Rate]

Because it is difficult to measure the maximum compression deformation rate of a powder, the maximum compression deformation rate of the aerogel composite powder in the present embodiments is determined through measurement of the maximum compression deformation rate of an aerogel composite block before crushing, which is described later. The maximum compression deformation rate at 25° C. can be 80% or higher, and may be 83% or higher or 86% or higher. It becomes easier to obtain superior strength, superior flexibility against deformation, and the like by setting the maximum compression deformation rate to 80% or higher. The upper limit of the maximum compression deformation rate is not limited in any way, and can be, for example, 90%.

The compression modulus, deformation recovery rate, and maximum compression deformation rate can be measured by using the compact table-top tester “EZ Test” (produced by Shimadzu Corporation, product name). Summary of a method for measuring compression modulus and so on by using the compact table-top tester is as follows.

(Preparation of Measurement Sample)

The aerogel composite block is processed into a cube (dice) of 7.0×7.0×7.0 mm by using a blade with a blade angle of approximately 20 to 25 degrees, and the cube is used as a measurement sample. Subsequently, the measurement sample is shaped with a sand paper of #1500 or finer to thoroughly smooth the surface, as necessary. Before measurement, the measurement sample is dried by using the thermostatic dryer “DVS402” (produced by Yamato Scientific Co., Ltd., product name) under the atmospheric pressure at 100° C. for 30 minutes. The measurement sample is then transferred into a desiccator and cooled to 25° C. Thus, a measurement sample for measurement of the compression modulus, deformation recovery rate, and maximum compression deformation rate is obtained.

(Measurement Method)

A load cell of 500 N is used. An upper platen (ϕ20 mm) and lower platen (ϕ118 mm) each made of stainless steel are used as jigs for compression measurement. The measurement sample is set between the jigs, and compressed at a speed of 1 mm/min, and, for example, the change in size of the measurement sample at 25° C. is measured. The measurement is terminated at a point of time when a load of higher than 500 N is applied or when the measurement sample is broken. Here, the compressive strain, ε, can be determined by using the following equation:

ε=Δd/d1

wherein Δd denotes the change in thickness (mm) of the measurement sample caused by a load; and d1 denotes the thickness (mm) of the measurement sample before application of a load.

The compressive stress (MPa), a, can be determined by using the following equation:

σ=F/A

wherein F denotes compressive force (N); and A denotes the cross-sectional area (mm²) of the measurement sample before application of a load.

The compression modulus (MPa), E, can be determined, for example, in a range of compressive force from 0.1 to 0.2 N by using the following equation:

E=(σ₂−σ₁)/(ε₂−ε₁)

wherein σ₁ denotes compressive stress (MPa) measured at a compressive force of 0.1 N; σ₂ denotes compressive stress (MPa) measured at a compressive force of 0.2 N; ε₁ denotes compressive strain measured at a compressive stress of σ₁; and ε₂ denotes compressive strain measured at a compressive stress of σ₂.

The deformation recovery rate and maximum compression deformation rate can be determined in accordance with the following equations:

Deformation recovery rate=(d3−d2)/(d1−d2)×100

Maximum compression deformation rate=(d1−d2)/d1×100

wherein d1 denotes the thickness of the measurement sample before application of a load; d2 denotes the thickness of the measurement sample at a point of time when a load of higher than 500 N is applied or when the measurement sample is broken; and d3 denotes the thickness of the measurement sample after removal of a load.

The thermal conductivity, compression modulus, deformation recovery rate, and maximum compression deformation rate can be appropriately adjusted, by changing conditions for production or raw materials or the like of the aerogel composite powder, which are described later.

[Density and Porosity]

The size of the pore 3, namely, the average pore diameter, in the aerogel composite powder in the present embodiments can be 5 to 1000 nm, and may be 25 to 500 nm. It becomes easier to obtain an aerogel composite powder superior in flexibility by setting the average pore diameter to 5 nm or larger, and it becomes easier to obtain an aerogel composite powder superior in thermal insulation by setting the average pore diameter to 1000 nm or smaller.

The density of the aerogel composite powder in the present embodiments at 25° C. can be 0.05 to 0.25 g/cm³, and may be 0.1 to 0.2 g/cm³. More superior strength and flexibility can be obtained by setting the density to 0.05 g/cm³ or higher, and more superior thermal insulation can be obtained by setting the density to 0.25 g/cm³ or lower.

The porosity of the aerogel composite powder in the present embodiments at 25° C. can be 85 to 95%, and may be 87 to 93%. More superior thermal insulation can be obtained by setting the porosity to 85% or higher, and more superior strength and flexibility can be obtained by setting the porosity to 95% or lower.

The average pore diameter, density, and porosity of the aerogel composite powder, with regard to the pore (through-hole) connected as a three-dimensional network, can be measured by using mercury porosimetry in accordance with DIN 66133. As the measurement apparatus, for example, an AutoPore IV9520 (produced by Shimadzu Corporation, product name) can be used.

[Shape of Powder]

The shape of the aerogel composite powder in the present embodiments is not limited in any way, and may be any of various shapes. Since the aerogel composite powder in the present embodiments has been crushed for powdering, as described later, the shape of the powder is typically an irregular shape with unevenness in the surface. Needless to say, the shape of the powder may be, for example, spherical. Alternatively, the shape of the powder may be in the form of a panel, a flake, or a fiber. The shape of the powder can be determined through direct observation of the aerogel composite powder by using SEM.

[Average Particle Diameter of Powder]

The average particle diameter D50 of the aerogel composite powder in the present embodiments can be 1 to 1000 μm, and may be 3 to 700 μm or 5 to 500 μm. It becomes easier to obtain an aerogel composite powder superior in dispersibility, handleability, and so on by setting the average particle diameter D50 of the aerogel composite powder to 1 μm or larger. On the other hand, it becomes easier to obtain an aerogel composite powder superior in dispersibility by setting the average particle diameter D50 to 1000 μm or smaller. The average particle diameter of the powder can be appropriately adjusted through the crushing method and conditions for crushing, and the manner of sieving, classification, or the like.

The average particle diameter D50 of the powder can be measured by using a laser diffraction/scattering method. For example, the aerogel composite powder is added to a solvent (ethanol) to a concentration in the range of 0.05 to 5% by mass, and the resultant is vibrated with a 50 W ultrasonic homogenizer for 15 to 30 minutes to disperse the powder. Thereafter, approximately 10 mL of the dispersion is injected into a laser diffraction/scattering particle size distribution analyzer, and the particle diameter is measured at 25° C. with a refractive index of 1.3 and absorption of 0. And then, a particle diameter at 50% of the cumulative value (volume-based) in the particle size distribution is used as the average particle diameter, D50. For the measurement apparatus, for example, a Microtrac MT3000 (produced by Nikkiso Co., Ltd., product name) can be used.

<Specific Modes of Aerogel Component>

The aerogel composite powder in the present embodiments can comprise polysiloxane having a main chain including siloxane bonds (Si—O—Si). The aerogel composite can include, as a structural unit, the following unit M, unit D, unit T, or unit Q.

In the formulas, R represents an atom (e.g., hydrogen atom) or atom group (e.g., alkyl group) bonding to a silicon atom. The unit M is a unit consisting of a monovalent group in which a silicon atom is bonding to one oxygen atom. The unit D is a unit consisting of a divalent group in which a silicon atom is bonding to two oxygen atoms. The unit T is a unit consisting of a trivalent group in which a silicon atom is bonding to three oxygen atoms. The unit Q is a unit consisting of a tetravalent group in which a silicon atom is bonding to four oxygen atoms. Information on the contents of these units can be acquired through Si-NMR.

Examples of the aerogel component of the aerogel composite powder in the present embodiments include modes described below. Use of any of these modes facilitates control of the thermal insulation and flexibility of the aerogel composite powder to desired levels. However, use of any of these modes is not necessarily intended to obtain the aerogel composite powder specified in the present embodiments. By using any of these modes, an aerogel composite powder having thermal conductivity and compression modulus corresponding to the mode can be obtained. Accordingly, an aerogel composite powder having thermal insulation and flexibility suitable for an intended application can be provided.

(First Mode)

The aerogel composite powder in the present embodiments can have a structure represented by the following formula (1). The aerogel composite powder in the present embodiments can have a structure represented by the following formula (1a), as the structure including a structure represented by the formula (1).

In the formulas (1) and (1a), R¹ and R² each independently represent an alkyl group or an aryl group, and R³ and R⁴ each independently represent an alkylene group. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, and a cyano group. p represents an integer of 1 to 50. In the formula (1a), two or more groups as R¹ may be identical or different, and, similarly, two or more groups as R² may be identical or different. In the formula (1a), two or more groups as R³ may be identical or different, and, similarly, two or more groups as R⁴ may be identical or different.

Through introduction of the structure represented by the formula (1) or (1a), as the aerogel component, into the skeleton of the aerogel composite powder, the aerogel composite powder is provided with low thermal conductivity and becomes flexible. From such a viewpoint, R¹ and R² in the formulas (1) and (1a) are, in one example, each independently an alkyl group having one to six carbon atoms, a phenyl group, or another group, and examples of this alkyl group include a methyl group. R³ and R⁴ in the formulas (1) and (1a) are, in one example, each independently an alkylene group having one to six carbon atoms or another group, and examples of this alkylene group include an ethylene group and a propylene group. In the formula (1a), p can be 2 to 30, and may be 5 to 20.

(Second Mode)

The aerogel composite powder in the present embodiments has a ladder-type structure including struts and a bridge, wherein the bridge can have a structure represented by the following formula (2). Through introduction of such a ladder-type structure, as the aerogel component, into the skeleton of the aerogel composite powder, the heat resistance and mechanical strength can be improved. In the present embodiments, “ladder-type structure” is a structure including two struts and bridges each connecting the struts (a structure having the form of what is called “ladder”). In the present mode, the skeleton of the aerogel composite may consist of the ladder-type structure, and the aerogel composite powder may partially have the ladder-type structure.

In the formula (2), R⁵ and R⁶ each independently represent an alkyl group or an aryl group, and b represents an integer of 1 to 50. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, and a cyano group. When b is an integer of 2 or more in the formula (2), two or more groups as R⁵ may be identical or different, and, similarly, two or more groups as R⁶ may be identical or different.

Through introduction of the above structure, as the aerogel component, into the skeleton of the aerogel composite powder, for example, the aerogel composite powder is provided with flexibility superior to that of aerogel having a structure derived from conventional ladder-type silsesquioxane (i.e., having a structure represented by the following formula (X)). Silsesquioxane is a polysiloxane having the composition formula (RSiO_(1.5))_(n), and can have various skeleton structures such as those of cage-type, ladder-type, and random-type. While the structure of a bridge in aerogel having a structure derived from conventional ladder-type silsesquioxane is —O— (the aerogel includes the above unit T as a structural unit), as represented by the following formula (X), the structure of a bridge in the aerogel composite powder in the present mode is the structure represented by the above formula (2) (polysiloxane structure). However, the aerogel composite powder in the present mode may have a structure derived from silsesquioxane in addition to the structure represented by the formula (2).

In the formula (X), R represents a hydroxy group, an alkyl group, or an aryl group.

The structure forming each strut and the chain length thereof, and the interval in the structure forming bridges are not limited in any way, and the ladder-type structure may be a ladder-type structure represented by the following formula (3) to further improve heat resistance and mechanical strength.

In the formula (3), R⁵, R⁶, R⁷ and R⁸ each independently represent an alkyl group or an aryl group; a and c each independently represent an integer of 1 to 3000; and b represents an integer of 1 to 50. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, and a cyano group. When b is an integer of 2 or more in the formula (3), two or more groups as R⁵ may be identical or different, and, similarly, two or more groups as R⁶ may be identical or different. When a is an integer of 2 or more in the formula (3), two or more groups as R⁷ may be identical or different, and, similarly, when c is an integer of 2 or more, two or more groups as R⁸ may be identical or different.

To obtain more superior flexibility, R⁵, R⁶, R⁷ and R⁸ in the formulas (2) and (3) (R⁷ and R⁸ are only in the formula (3)) are, in one example, each independently an alkyl group having one to six carbon atoms, a phenyl group, or another group, and examples of this alkyl group include a methyl group. In the formula (3), a and c can be each independently 6 to 2000, and may be each independently 10 to 1000. In the formulas (2) and (3), b can be 2 to 30, and may be 5 to 20.

(Third Mode)

The aerogel composite powder in the present embodiments may be a dried product of a wet gel as a condensate of a sol (a product derived by drying a wet gel formed from the sol: a dried product of a wet gel derived from the sol) comprising: a silica particle; and at least one selected from the group consisting of a silicon compound having a hydrolyzable functional group or a condensable functional group (in the molecule) and a hydrolysis product of the silicon compound having a hydrolyzable functional group. Also the aerogel composite described hereinbefore may be a product derived by drying a wet gel formed from a sol comprising a silica particle and a silicon compound or the like as described here.

A silicon compound other than polysiloxane compounds, which are described later, can be used as the silicon compound having a hydrolyzable functional group or a condensable functional group. In other words, the sol can comprise at least one compound selected from the group consisting of a silicon compound having a hydrolyzable functional group or a condensable functional group (except polysiloxane compounds) and a hydrolysis product of the silicon compound having a hydrolyzable functional group (hereinafter, occasionally referred to as “group of silicon compounds”). The number of silicon atoms in the molecule of the silicon compound can be 1 or 2.

The silicon compound having a hydrolyzable functional group is not limited in any way, and examples thereof include alkylsilicon alkoxide. The number of hydrolyzable functional groups of the alkylsilicon alkoxide can be three or less to improve the water resistance. Examples of such alkylsilicon alkoxide include monoalkyltrialkoxysilane, monoalkyldialkoxysilane, dialkyldialkoxysilane, mono alkylmonoalkoxysilane, and dialkylmonoalkoxysilane, trialkylmonoalkoxysilane, specifically methyltrimethoxysilane, methyldimethoxysilane, dimethyldimethoxysilane, and ethyltrimethoxysilane. Examples of the hydrolyzable functional group include an alkoxy group such as a methoxy group and an ethoxy group.

The silicon compound having a condensable functional group is not limited in any way, and examples thereof include silanetetraol, methylsilanetriol, dimethylsilanediol, phenylsilanetriol, phenylmethylsilanediol, diphenylsilanediol, n-propylsilanetriol, hexylsilanetriol, octylsilanetriol, decylsilanetriol, and trifluoropropylsilanetriol.

The silicon compound having a hydrolyzable functional group or a condensable functional group may further have a reactive group different from a hydrolyzable functional group and a condensable functional group (a functional group corresponding to none of hydrolyzable functional groups and condensable functional groups). Examples of the reactive group include an epoxy group, a mercapto group, a glycidoxy group, a vinyl group, an acryloyl group, a methacryloyl group, and an amino group. The epoxy group may be included in an epoxy group-containing group such as a glycidoxy group.

Also applicable as a silicon compound having a reactive group in which the number of hydrolyzable functional groups is three or less are, for example, vinyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-methacryloxypropyltrimethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropylmethyldimethoxysilane, N-phenyl-3-aminopropyltrimethoxysilane, and N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane.

Also applicable as a silicon compound having a condensable functional group and a reactive functional group are, for example, vinyl silanetriol, 3-glycidoxypropylsilanetriol, 3-glycidoxypropylmethylsilanediol, 3-methacryloxypropylsilanetriol, 3-methacryloxypropylmethylsilanediol, 3-acryloxypropylsilanetriol, 3-mercaptopropylsilanetriol, 3-mercaptopropylmethylsilanediol, N-phenyl-3-aminopropylsilanetriol, and N-2-(aminoethyl)-3-aminopropylmethylsilanediol.

In addition, bis(trimethoxysilyl)methane, bis(trimethoxysilyl) ethane, bis(trimethoxysilyl)hexane, ethyltrimethoxysilane, vinyltrimethoxysilane, etc., each as a silicon compound in which the number of hydrolyzable functional groups at molecular ends is three or less are also applicable.

The silicon compound having a hydrolyzable functional group or a condensable functional group (except polysiloxane compounds) and hydrolysis product of the silicon compound having a hydrolyzable functional group may be used singly, or as a mixture of two or more.

In production of the aerogel composite powder in the present embodiments, the silicon compound can comprise a polysiloxane compound having a hydrolyzable functional group or a condensable functional group. In other words, the sol comprising the silicon compound can further comprise at least one selected from the group consisting of a polysiloxane compound having a hydrolyzable functional group or a condensable functional group (in the molecule) and a hydrolysis product of the polysiloxane compound having a hydrolyzable functional group (hereinafter, occasionally referred to as “group of polysiloxane compounds”).

The functional group of the polysiloxane compound or the like is not limited in any way, and can be a group reactive with the same functional group or reactive with another functional group. Examples of the hydrolyzable functional group include an alkoxy group. Examples of the condensable functional group include a hydroxy group, a silanol group, a carboxy group, and a phenolic hydroxy group. The hydroxy group may be included in a hydroxy group-containing group such as a hydroxyalkyl group. The polysiloxane compound having a hydrolyzable functional group or a condensable functional group may further have the above-described reactive group different from a hydrolyzable functional group and a condensable functional group (a functional group corresponding to none of hydrolyzable functional groups and condensable functional groups). The polysiloxane compound having the functional group and reactive group may be used singly, or as a mixture of two or more. Examples of the functional group and reactive group as a group to improve the flexibility of the aerogel composite include an alkoxy group, a silanol group, and hydroxyalkyl group, and the alkoxy group and hydroxyalkyl group among them can further improve the compatibility of the sol. For improvement of the reactivity of the polysiloxane compound and reduction of the thermal conductivity of the aerogel composite powder, the number of carbon atoms of the alkoxy group or hydroxyalkyl group can be 1 to 6, and may be 2 to 4 for further improvement of the flexibility of the aerogel composite powder.

Examples of the polysiloxane compound having a hydroxyalkyl group include those having a structure represented by the following formula (A). By using the polysiloxane compound having a structure represented by the following formula (A), the structures represented by the above formulas (1) and (1a) can be introduced into the skeleton of the aerogel composite powder.

In the formula (A), R^(1a) represents a hydroxyalkyl group; R^(2a) represents an alkylene group; R^(3a) and R^(4a) each independently represent an alkyl group or an aryl group; and n represents an integer of 1 to 50. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, and a cyano group. In the formula (A), two groups as R^(1a) may be identical or different, and, similarly, two groups as R^(2a) may be identical or different. In the formula (A), two or more groups as R^(3a) may be identical or different, and, similarly, two or more groups as R^(4a) may be identical or different.

It becomes much easier to obtain an aerogel composite powder having low thermal conductivity and being flexible by using a wet gel as a condensate of the sol (or formed from the sol) comprising the polysiloxane compound having the above structure. From such a viewpoint, R^(1a) in the formula (A) is, in one example, a hydroxyalkyl group having one to six carbon atoms, and examples of this hydroxyalkyl group include a hydroxyethyl group and a hydroxypropyl group. R^(2a) in the formula (A) is, in one example, an alkylene group having one to six carbon atoms, and examples of this alkylene group include an ethylene group and a propylene group. R^(3a) and R^(4a) in the formula (A) are, in one example, each independently an alkyl group having one to six carbon atoms, a phenyl group, or another group, and examples of this alkyl group include a methyl group. In the formula (A), n can be 2 to 30, and may be 5 to 20.

A commercially available product can be used as the polysiloxane compound having the structure represented by the above formula (A), and examples thereof include compounds including X-22-160AS, KF-6001, KF-6002, and KF-6003 (all produced by Shin-Etsu Chemical Co., Ltd.) and compounds including XF42-B0970 and Fluid OFOH 702-4% (all produced by Momentive Performance Materials Inc.).

Examples of the polysiloxane compound having an alkoxy group include those having a structure represented by the following formula (B). By using the polysiloxane compound having a structure represented by the following formula (B), the ladder-type structure with bridges represented by the above formula (2) can be introduced into the skeleton of the aerogel composite powder.

In the formula (B), R^(1b) represents an alkyl group, an alkoxy group, or an aryl group; R^(2b) and R^(3b) each independently represent an alkoxy group; R^(4b) and R^(5b) each independently represent an alkyl group or an aryl group; and m represents an integer of 1 to 50. Here, examples of the aryl group include a phenyl group and a substituted phenyl group. Examples of the substituent of the substituted phenyl group include an alkyl group, a vinyl group, a mercapto group, an amino group, a nitro group, and a cyano group. In the formula (B), two groups as R^(1b) may be identical or different, two groups as R^(2b) may be identical or different, and, similarly, two groups as R^(3b) may be identical or different. When m is an integer of 2 or more in the formula (B), two or more groups as R^(4b) may be identical or different, and, similarly, two or more groups as R^(5b) may be identical or different.

It becomes much easier to obtain an aerogel composite powder having low thermal conductivity and being flexible by using a wet gel as a condensate of the sol (or formed from the sol) comprising the polysiloxane compound having the above structure or a hydrolysis product thereof. From such a viewpoint, R^(1b) in the formula (B) is, in one example, an alkyl group having one to six carbon atoms or an alkoxy group having one to six carbon atoms, and examples of this alkyl group or alkoxy group include a methyl group, a methoxy group, and an ethoxy group. R^(2b) and R^(3b) in the formula (B) are, in one example, each independently an alkoxy group having one to six carbon atoms, and examples of this alkoxy group include a methoxy group and an ethoxy group. R^(4b) and R^(5b) in the formula (B) are, in one example, each independently an alkyl group having one to six carbon atoms, a phenyl group, or another group, and examples of this alkyl group include a methyl group. In the formula (B), m can be 2 to 30, and may be 5 to 20.

The polysiloxane compound having the structure represented by the above formula (B) can be obtained appropriately with reference, for example, to any of production methods reported in Japanese Unexamined Patent Publication No. 2000-26609 and Japanese Unexamined Patent Publication No. 2012-233110.

Since an alkoxy group is hydrolyzable, the polysiloxane compound having an alkoxy group is possibly present as a hydrolysis product in the sol, and the polysiloxane compound having an alkoxy group and a hydrolysis product thereof may coexist. In the polysiloxane compound having an alkoxy group, alkoxy groups in the molecule may be totally hydrolyzed or partially hydrolyzed.

The polysiloxane compound having a hydrolyzable functional group or a condensable functional group and hydrolysis product of the polysiloxane compound having a hydrolyzable functional group may be used singly, or as a mixture of two or more.

The content of the group of silicon compounds (the sum total of the content of the silicon compound having a hydrolyzable functional group or a condensable functional group and the content of the hydrolysis product of the silicon compound having a hydrolyzable functional group) comprised in the sol can be 5 parts by mass or more, and may be 10 parts by mass or more, with respect to 100 parts by mass of the total amount of the sol. The content can be 50 parts by mass or less, and may be 30 parts by mass or less, with respect to 100 parts by mass of the total amount of the sol. In other words, the content of the group of silicon compounds can be 5 to 50 parts by mass, and may be 10 to 30 parts by mass, with respect to 100 parts by mass of the total amount of the sol. It becomes easier to obtain better reactivity by setting the content to 5 parts by mass or more, and it becomes easier to obtain better compatibility by setting the content to 50 parts by mass or less.

When the sol further comprises the polysiloxane compound, the sum total of the content of the group of silicon compounds and the content of the group of polysiloxane compounds (the sum total of the content of the polysiloxane compound having a hydrolyzable functional group or a condensable functional group and the content of the hydrolysis product of the polysiloxane compound having a hydrolyzable functional group) can be 5 parts by mass or more, and may be 10 parts by mass or more, with respect to 100 parts by mass of the total amount of the sol. The sum total of the contents can be 50 parts by mass or less, and may be 30 parts by mass or less, with respect to 100 parts by mass of the total amount of the sol. In other words, the sum total of the contents can be 5 to 50 parts by mass, and may be 10 to 30 parts by mass, with respect to 100 parts by mass of the total amount of the sol. It becomes much easier to obtain better reactivity by setting the sum total of the contents to 5 parts by mass or more, and it becomes much easier to obtain better compatibility by setting the sum total of the contents to 50 parts by mass or less. In this case, the ratio of the content of the group of silicon compounds to the content of the group of polysiloxane compounds can be 0.5:1 to 4:1, and may be 1:1 to 2:1. It becomes much easier to obtain better compatibility by setting the ratio of the contents of these compounds to 0.5:1 or higher, and it becomes much easier to prevent the gel from shrinking by setting the ratio of the contents of these compounds to 4:1 or lower.

The content of the silica particle comprised in the sol can be 1 part by mass or more, and may be 4 parts by mass or more, with respect to 100 parts by mass of the total amount of the sol. The content can be 20 parts by mass or less, and may be 15 parts by mass or less, with respect to 100 parts by mass of the total amount of the sol. In other words, the content of the silica particle can be 1 to 20 parts by mass, and may be 4 to 15 parts by mass, with respect to 100 parts by mass of the total amount of the sol. It becomes easier to impart moderate strength to aerogel and obtain an aerogel composite powder superior in shrinkage resistance in drying by setting the content to 1 part by mass or more. It becomes easier to suppress the solid thermal conduction of the silica particle and obtain an aerogel composite powder superior in thermal insulation by setting the content to 20 parts by mass or less.

(Other Modes)

The aerogel composite powder in the present embodiments can have a structure represented by the following formula (4). The aerogel composite powder in the present embodiments can comprise the silica particle and simultaneously have a structure represented by the following formula (4).

In the formula (4), R⁹ represents an alkyl group. Examples of the alkyl group include an alkyl group having one to six carbon atoms, and examples of this alkyl group include a methyl group.

The aerogel composite powder in the present embodiments can have a structure represented by the following formula (5). The aerogel composite powder in the present embodiments can comprise the silica particle and simultaneously have a structure represented by the following formula (5).

In the formula (5), R¹⁰ and R¹¹ each independently represent an alkyl group. Here, examples of the alkyl group include an alkyl group having one to six carbon atoms, and examples of this alkyl group include a methyl group.

The aerogel composite powder in the present embodiments can have a structure represented by the following formula (6). The aerogel composite powder in the present embodiments can comprise the silica particle and simultaneously have a structure represented by the following formula (6).

In the formula (6), R¹² represents an alkylene group. Here, examples of the alkylene group include an alkylene group having 1 to 10 carbon atoms, and examples of this alkylene group include an ethylene group and a hexylene group.

<Method for Producing Aerogel Composite Powder>

Next, the method for producing an aerogel composite powder will be described. The method for producing an aerogel composite powder is not limited in any way, and an aerogel composite can be produced, for example, by using the following method.

Specifically, the aerogel composite powder in the present embodiments can be produced by using a production method primarily including: a step of forming a sol; a step of forming a wet gel, where the sol obtained in the step of forming a sol is gelled and then aged to obtain a wet gel; a step of washing and solvent displacement, where the wet gel obtained in the step of forming a wet gel is washed and subjected to solvent displacement (as necessary); a step of drying, where the wet gel washed and subjected to solvent displacement is dried; and a step of crushing a block, where an aerogel composite block obtained by drying is crushed.

Alternatively, the aerogel composite powder in the present embodiments can be produced by using a production method primarily including: a step of forming a sol; the step of forming a wet gel; a step of crushing a wet gel, where the wet gel obtained in the step of forming a wet gel is crushed; the step of washing and solvent displacement; and the step of drying.

The size of the aerogel composite powder obtained can be further homogenized by sieving, classification, or the like. If the size of the powder is uniformed, the handleability can be enhanced. “Sol” refers to a state before the occurrence of gelling reaction, and, in the present embodiments, a state in which the group of silicon compounds, optionally with the group of polysiloxane compounds, and the silica particle are dissolved or dispersed in a solvent. Wet gel refers to a gel solid in a wet state which contains a liquid medium but does not have fluidity.

Now, each step of the method for producing the aerogel composite powder in the present embodiments will be described.

(Step of Forming Sol)

The step of forming a sol is a step in which the above-described silicon compound, optionally with the polysiloxane compound, and the silica particle or a solvent containing the silica particle are mixed together for hydrolysis to form the sol. In this step, an acid catalyst may be further added into the solvent to accelerate hydrolysis reaction. As shown in Japanese Patent No. 5250900, a surfactant, a thermally-hydrolyzable compound, etc., can be added into the solvent. Moreover, a component such as carbon graphite, an aluminum compound, a magnesium compound, a silver compound, and a titanium compound may be added into the solvent, for example, for the purpose of suppressing radiation of heat rays.

For example, water or a mixed solution of water and an alcohol can be used as the solvent. Examples of the alcohol include methanol, ethanol, n-propanol, 2-propanol, n-butanol, 2-butanol, and t-butanol. Among them, alcohols with a low surface tension and low boiling point for reduction of the interfacial tension on a gel wall are, for example, methanol, ethanol, and 2-propanol. These may be used singly, or as a mixture of two or more thereof.

If an alcohol is used as the solvent, for example, the amount of the alcohol can be 4 to 8 mol, and may be 4 to 6.5 mol or 4.5 to 6 mol, with respect to 1 mol of the total amount of the group of silicon compounds and the group of polysiloxane compounds. It becomes much easier to obtain better compatibility by setting the amount of the alcohol to 4 mol or more, and it becomes much easier to prevent the gel from shrinking by setting the amount of the alcohol to 8 mol or less.

Examples of the acid catalyst include inorganic acids such as hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid, sulfurous acid, phosphoric acid, phosphorous acid, hypophosphorous acid, bromic acid, chloric acid, chlorous acid, and hypochlorous acid; acidic phosphates such as acidic aluminum phosphate, acidic magnesium phosphate, and acidic zinc phosphate; and organic carboxylic acids such as acetic acid, formic acid, propionic acid, oxalic acid, malonic acid, succinic acid, citric acid, malic acid, adipic acid, and azelaic acid. Among them, acid catalysts to further improve the water resistance of an aerogel composite to be obtained are, for example, organic carboxylic acids. Examples of such organic carboxylic acids include acetic acid; however, formic acid, propionic acid, oxalic acid, malonic acid, and so on are also acceptable. These may be used singly, or as a mixture of two or more thereof.

By using the acid catalyst, hydrolysis reaction of the silicon compound and the polysiloxane compound can be accelerated and the sol can be obtained in a shorter period of time.

The amount of the acid catalyst to be added can be 0.001 to 0.1 parts by mass with respect to 100 parts by mass of the total amount of the group of silicon compounds and the group of polysiloxane compounds.

For the surfactant, nonionic surfactant, ionic surfactant, or the like can be used. These may be used singly, or as a mixture of two or more thereof.

For the nonionic surfactant, for example, a compound including a hydrophilic moiety such as polyoxyethylene and a hydrophobic moiety primarily consisting of an alkyl group or a compound including a hydrophilic moiety such as polyoxypropylene can be used. Examples of the compound including a hydrophilic moiety such as polyoxyethylene and a hydrophobic moiety primarily consisting of an alkyl group include polyoxyethylene nonyl phenyl ether, polyoxyethylene octyl phenyl ether, and polyoxyethylene alkyl ether. Examples of the compound including a hydrophilic moiety such as polyoxypropylene include polyoxypropylene alkyl ether and a block copolymer of polyoxyethylene and polyoxypropylene.

Examples of the ionic surfactant include cationic surfactant, anionic surfactant, and amphoteric surfactant. Examples of the cationic surfactant include cetyltrimethylammonium bromide and cetyltrimethylammonium chloride, and examples of the anionic surfactant include sodium dodecylsulfonate. Examples of the amphoteric surfactant include amino acid-based surfactant, betaine-based surfactant, and amine oxide-based surfactant. Examples of the amino acid-based surfactant include acylglutamic acid. Examples of the betaine-based surfactant include betaine lauryldimethylaminoacetate and betaine stearyldimethylaminoacetate. Examples of the amine oxide-based surfactant include lauryldimethylamine oxide.

In the step of forming a wet gel, which is described later, these surfactants are inferred to act to reduce the difference in chemical affinity between a solvent and a growing siloxane polymer in the reaction system, and thereby prevent phase separation.

The amount of the surfactant to be added can be, for example, 1 to 100 parts by mass with respect to 100 parts by mass of the total amount of the group of silicon compounds and the group of polysiloxane compounds, although it depends on the type of the surfactant and the types and amounts of the group of silicon compounds and the group of polysiloxane compounds. The amount to be added may be 5 to 60 parts by mass.

The thermally-hydrolyzable compound is inferred to generate a base catalyst through thermal hydrolysis to basify the reaction solution, and accelerate sol-gel reaction in the step of forming a wet gel, which is described later. Hence, the thermally-hydrolyzable compound is not limited in any way as long as it is a compound capable of basifying the reaction solution after hydrolysis, and examples thereof include urea; acid amide such as formamide, N-methylformamide, N,N-dimethylformamide, acetamide, N-methylacetamide, and N,N-dimethylacetamide; and cyclic nitrogen compounds such as hexamethylenetetramine Among them, urea particularly satisfactorily provides the above accelerating effect.

The amount of the thermally-hydrolyzable compound to be added is not limited in any way as long as it is an amount such that sol-gel reaction can be sufficiently accelerated in the step of forming a wet gel, which is described later. When urea is used as the thermally-hydrolyzable compound, for example, the amount of urea to be added can be 1 to 200 parts by mass with respect to 100 parts by mass of the total amount of the group of silicon compounds and the group of polysiloxane compounds. The amount to be added may be 2 to 150 parts by mass. It becomes much easier to obtain good reactivity by setting the amount to be added to 1 part by mass or more, and it becomes much easier to prevent precipitation of crystals and lowering of gel density by setting the amount to be added to 200 parts by mass or less.

Hydrolysis in the step of forming a sol may be performed, for example, in a temperature environment of 20 to 60° C. for 10 minutes to 24 hours, and may be performed in a temperature environment of 50 to 60° C. for 5 minutes to 8 hours, although the conditions depend on the types and amounts of the silicon compound, polysiloxane compound, silica particle, acid catalyst, surfactant, etc., in the mixed solution. Thereby, the hydrolyzable functional groups in the silicon compound and polysiloxane compound are sufficiently hydrolyzed, and hence a hydrolysis product of the silicon compound and a hydrolysis product of the polysiloxane compound can be obtained more reliably.

When the thermally-hydrolyzable compound is added into the solvent, however, the temperature environment in the step of forming a sol may be controlled to a temperature such that the hydrolysis of the thermally-hydrolyzable compound is inhibited to prevent the sol from gelling. The temperature in this case may be any temperature such that the hydrolysis of the thermally-hydrolyzable compound can be inhibited. When urea is used as the thermally-hydrolyzable compound, for example, the temperature environment in the step of forming a sol can be 0 to 40° C., and may be 10 to 30° C.

(Step of Forming Wet Gel)

The step of forming a wet gel is a step in which the sol obtained in the step of forming a sol is gelled and then aged to obtain a wet gel. In this step, a base catalyst can be used to accelerate gelling.

Examples of the base catalyst include alkali metal hydroxides such as lithium hydroxide, sodium hydroxide, potassium hydroxide, and cesium hydroxide; ammonium compounds such as ammonium hydroxide, ammonium fluoride, ammonium chloride, and ammonium bromide; basic sodium phosphate such as sodium metaphosphate, sodium pyrophosphate, and sodium polyphosphate; aliphatic amines such as allylamine, diallylamine, triallylamine, isopropylamine, diisopropylamine, ethylamine, diethylamine, triethylamine, 2-ethylhexylamine, 3-ethoxypropylamine, diisobutylamine, 3-(diethylamino)propylamine, di-2-ethylhexylamine, 3-(dibutylamino)propylamine, tetramethylethylenediamine, t-butylamine, sec-butylamine, propylamine, 3-(methylamino)propylamine, 3-(dimethylamino)propyl amine, 3-methoxyamine, dimethylethanolamine, methyldiethanolamine, diethanolamine, and triethanolamine; nitrogen-containing heterocyclic compounds such as morpholine, N-methylmorpholine, 2-methylmorpholine, piperazine and derivatives thereof, piperidine and derivatives thereof, and imidazole and derivatives thereof. Among them, ammonium hydroxide (aqueous ammonia) is superior in that, as well as superiority in economic efficiency, it has high volatility and is less likely to remain in the aerogel composite powder after drying, and hence hardly deteriorates the water resistance. These base catalysts may be used singly, or as a mixture of two or more thereof.

By using the base catalyst, dehydration condensation reaction or dealcoholization condensation reaction of the silicon compound, polysiloxane compound, and silica particle in the sol can be accelerated to complete the gelling of the sol in a shorter period of time. Thereby, a wet gel with higher strength (rigidity) can be obtained. In particular, ammonia has high volatility and is less likely to remain in the aerogel composite powder, and hence an aerogel composite powder more superior in water resistance can be obtained by using ammonia as the base catalyst.

The amount of the base catalyst to be added can be 0.5 to 5 parts by mass, and may be 1 to 4 parts by mass, with respect to 100 parts by mass of the total amount of the group of silicon compounds and the group of polysiloxane compounds. Gelling can be completed in a shorter period of time by setting the amount of the base catalyst to be added to 0.5 parts by mass or more, and lowering of the water resistance can be more reduced by setting the amount to 5 parts by mass or less.

Gelling of the sol in the step of forming a wet gel may be performed in an airtight container so as not to allow the solvent and base catalyst to volatile. The gelling temperature can be 30 to 90° C., and may be 40 to 80° C. Gelling can be completed in a shorter period of time and a wet gel with higher strength (rigidity) can be obtained by setting the gelling temperature to 30° C. or higher. It becomes easier to suppress the volatilization of the solvent (in particular, an alcohol) by setting the gelling temperature to 90° C. or lower, and hence gelling can be completed while volume shrinkage is prevented.

Aging in the step of forming a wet gel may be performed in an airtight container so as not to allow the solvent and base catalyst to volatize. Aging strengthens the bonding of the components constituting a wet gel, and as a result a wet gel with sufficiently high strength (rigidity) for preventing shrinkage in drying can be obtained. The aging temperature can be 30 to 90° C., and may be 40 to 80° C. A wet gel with higher strength (rigidity) can be obtained by setting the aging temperature to 30° C. or higher, and it becomes easier to suppress the volatilization of the solvent (in particular, an alcohol) by setting the aging temperature to 90° C. or lower, and hence gelling can be completed while volume shrinkage is prevented.

It is often difficult to determine when the gelling of the sol is completed, and hence gelling and subsequent aging of the sol may be sequentially performed in a series of operations.

The gelling time and aging time depend on the gelling temperature and aging temperature; however, the silica particle is comprised in the sol in the present embodiments, and as a result, in particular, the gelling time can be reduced as compared with conventional methods for producing aerogel. The reason is presumably that silanol groups or reactive groups possessed by the silicon compound, polysiloxane compound, etc., in the sol form hydrogen bonding or chemical bonding with silanol groups of the silica particle. The gelling time can be 10 to 120 minutes, and may be 20 to 90 minutes. It becomes easier to obtain a more homogeneous wet gel by setting the gelling time to 10 minutes or longer, and the steps from the step of washing and solvent displacement to the step of drying, which are described later, can be simplified by setting the gelling time to 120 minutes or shorter. The total time of the gelling time and aging time, as a total of the step of gelling and aging, can be 4 to 480 hours, and may be 6 to 120 hours. A wet gel with higher strength (rigidity) can be obtained by setting the total of the gelling time and aging time to 4 hours or longer, and it becomes easier to maintain the effect of aging by setting the total of the gelling time and aging time to 480 hours or shorter.

To impart a lower density or a larger average pore diameter to an aerogel composite powder to be obtained, the gelling temperature and aging temperature may be raised within the above range or the total time of the gelling time and aging time may be prolonged within the above range. Alternatively, to impart a higher density or a smaller average pore diameter to an aerogel composite powder to be obtained, the gelling temperature and aging temperature may be lowered within the above range or the total time of the gelling time and aging time may be shortened within the above range.

(Step of Crushing Wet Gel)

When the step of crushing a wet gel is performed, the wet gel obtained in the step of forming a wet gel is crushed. For crushing, for example, the wet gel is placed in a Henschel mixer or the step of forming a wet gel is performed in a mixer, and the mixer is operated under moderate conditions (rotational frequency and duration). For crushing, more simply, the wet gel is placed in a sealable container or the step of forming a wet gel is performed in a sealable container, and the wet gel is shaken for a moderate duration with a shaking apparatus such as a shaker. As necessary, the particle diameter of the wet gel can be adjusted by using, a jet mill, a roller mill, a bead mill, or the like.

(Step of Washing and Solvent Displacement)

The step of washing and solvent displacement is a step including a substep of washing the wet gel obtained in the step of forming a wet gel or the step of crushing a wet gel (a substep of washing) and a substep of displacing the washing solution in the wet gel with a solvent suitable for conditions for drying (in the step of drying described later) (a substep of solvent displacement). Although the step of washing and solvent displacement can be performed in a manner such that the substep of washing the wet gel is not performed and only the substep of solvent displacement is performed, the wet gel may be washed to reduce impurities including unreacted matters and byproducts in the wet gel and enable production of an aerogel composite powder having higher purity. In the present embodiments, the substep of solvent displacement after the substep of washing is not necessarily essential, as described later, because the silica particle is comprised in the gel.

In the substep of washing, the wet gel obtained in the step of forming a wet gel or the step of crushing a wet gel is washed. This washing can be performed repeatedly, for example, by using water or an organic solvent. In washing, the washing efficiency can be improved by heating.

For the organic solvent, various organic solvents can be used, such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, acetone, methyl ethyl ketone, 1,2-dimethoxyethane, acetonitrile, hexane, toluene, diethyl ether, chloroform, ethyl acetate, tetrahydrofuran, methylene chloride, N,N-dimethylformamide, dimethylsulfoxide, acetic acid, and formic acid. These organic solvents may be used singly, or as a mixture of two or more thereof.

In the substep of solvent displacement, which is described later, a solvent with low surface tension can be used to prevent the gel from shrinking due to drying. However, solvents with low surface tension generally have extremely low mutual solubility with water. For this reason, the organic solvent used for the substep of washing when a solvent with low surface tension is used in the substep of solvent displacement is, for example, a hydrophilic organic solvent having high mutual solubility with both water and the solvent with low surface tension. The hydrophilic organic solvent used in the substep of washing can serve for pre-displacement for the substep of solvent displacement. Examples of the hydrophilic organic solvent include, among the above organic solvents, methanol, ethanol, 2-propanol, acetone, and methyl ethyl ketone. Methanol, ethanol, methyl ethyl ketone, etc., are superior in economic efficiency.

The amount of water or the organic solvent used in the substep of washing can be an amount such that the solvent in the wet gel can be sufficiently displaced and washed out. The amount can be 3 to 10 times the volume of the wet gel. Washing can be repeated until the moisture content of the wet gel after washing reaches 10% by mass or less to the mass of silica.

The temperature environment in the substep of washing can be a temperature equal to or lower than the boiling point of the solvent used for washing, and, when methanol is used, for example, heating can be performed at a temperature of around 30 to 60° C.

In the substep of solvent displacement, the solvent of the wet gel washed is displaced with a specific solvent for displacement to prevent shrinkage in the step of drying, which is described later. Then, the efficiency of displacement can be improved by heating. Specifically, when drying is performed under the atmospheric pressure at a temperature lower than the critical point of the solvent used in drying in the step of drying, the solvent for displacement is, for example, a solvent with low surface tension, which is described later. When supercritical drying is performed, on the other hand, the solvent for displacement is, for example, ethanol, methanol, 2-propanol, dichlorodifluoromethane, carbon dioxide, or a mixed solvent of two or more of them.

Examples of the solvent with low surface tension include solvents with a surface tension of 30 mN/m or lower at 20° C. The surface tension may be 25 mN/m or lower or 20 mN/m or lower. Examples of the solvent with low surface tension include aliphatic hydrocarbons such as pentane (15.5), hexane (18.4), heptane (20.2), octane (21.7), 2-methylpentane (17.4), 3-methylpentane (18.1), 2-methylhexane (19.3), cyclopentane (22.6), cyclohexane (25.2), and 1-pentene (16.0); aromatic hydrocarbons such as benzene (28.9), toluene (28.5), m-xylene (28.7), and p-xylene (28.3); halogenated hydrocarbons such as dichloromethane (27.9), chloroform (27.2), carbon tetrachloride (26.9), 1-chloropropane (21.8), and 2-chloropropane (18.1); ethers such as ethyl ether (17.1), propyl ether (20.5), isopropyl ether (17.7), butyl ethyl ether (20.8), and 1,2-dimethoxyethane (24.6); ketones such as acetone (23.3), methyl ethyl ketone (24.6), methyl propyl ketone (25.1), and diethyl ketone (25.3); and esters such as methyl acetate (24.8), ethyl acetate (23.8), propyl acetate (24.3), isopropyl acetate (21.2), isobutyl acetate (23.7), and ethyl butyrate (24.6), where a numerical value in each parenthesis indicates surface tension at 20° C., and the unit is [mN/m]. Among them, aliphatic hydrocarbons (e.g., hexane, heptane) have low surface tension, and are superior in terms of the working environment. In addition, hydrophilic organic solvents among the above solvents, such as acetone, methyl ethyl ketone, and 1,2-dimethoxyethane, can simultaneously serve as the organic solvent for the substep of washing, if used. A solvent with a boiling point of 100° C. or lower at ambient pressure among the above solvents may be used because of easiness in drying in the step of drying, which is described later. The above solvents may be used singly, or as a mixture of two or more thereof.

The amount of the solvent to be used in the substep of solvent displacement can be an amount such that the solvent in the wet gel after washing can be sufficiently displaced. The amount can be 3 to 10 times the volume of the wet gel.

The temperature environment in the substep of solvent displacement can be a temperature equal to or lower than the boiling point of the solvent used for displacement, and, when heptane is used, for example, heating can be performed at a temperature of around 30 to 60° C.

In the present embodiments, the substep of solvent displacement is not necessarily essential, as described above, because the silica particle is comprised in the gel. The mechanism is inferred as follows: while the solvent of the wet gel is, in conventional methods, displaced with a specific solvent for displacement (a solvent with low surface tension) to prevent shrinkage in the step of drying, the silica particle functions as a support for the three-dimensional network skeleton and the skeleton is supported in the present embodiments, and the shrinkage of the gel in the step of drying is prevented; therefore, the gel can be subjected directly to the step of drying without displacement of the solvent used in washing. As described above, the steps from the step of washing and solvent displacement to the step of drying can be simplified in the present embodiments. However, the present embodiments never exclude implementation of the substep of solvent displacement.

(Step of Drying)

In the step of drying, the wet gel washed and (as necessary) subjected to solvent displacement as described above is dried. Thereby, an aerogel composite block or powder is obtained. That is, an aerogel derived by drying the wet gel formed from the above sol can be obtained.

The technique for drying is not limited in any way, and known ambient pressure drying, supercritical drying, or freeze drying can be used. Among them, ambient pressure drying or supercritical drying can be used for easiness in production of an aerogel composite block or powder having low density. To enable production at low cost, ambient pressure drying can be used. In the present embodiments, ambient pressure refers to 0.1 MPa (atmospheric pressure).

The aerogel composite block or powder can be obtained by drying the wet gel washed and (as necessary) subjected to solvent displacement under the atmospheric pressure at a temperature lower than the critical point of the solvent used in drying. The drying temperature, which depends on the type of the solvent used for displacement (the solvent used in washing, for the case without solvent displacement), can be 20 to 150° C. in consideration that drying at high temperature particularly increases the evaporation rate of the solvent and in some cases generates a large crack in the gel. The drying temperature may be 60 to 120° C. The drying time depends on the volume of the wet gel and the drying temperature, and can be 4 to 120 hours. In the present embodiments, acceleration of drying by applying a pressure lower than the critical point in a manner such that the productivity is not lowered is also encompassed in the concept of ambient pressure drying.

Alternatively, the aerogel composite block or powder can be obtained by applying supercritical drying to the wet gel washed and (as necessary) subjected to solvent displacement. Supercritical drying can be performed by using a known technique. Examples of the method for supercritical drying include a method of removing the solvent contained in the wet gel at a temperature and pressure equal to or higher than the critical point of the solvent. Another example of the method for supercritical drying is a method in which the wet gel is soaked in liquified carbon dioxide, for example, under conditions of around 20 to 25° C. and 5 to 20 MPa to totally or partially displace the solvent contained in the wet gel with carbon dioxide, which has a critical point lower than the solvent, and single carbon dioxide or a mixture of carbon dioxide and the solvent is then removed.

The aerogel composite block or powder obtained through ambient drying or supercritical drying as describe above may be further subjected to additional drying under ambient pressure at 105 to 200° C. for about 0.5 to 2 hours. Thereby, it becomes much easier to obtain an aerogel composite having low density and small pores. The additional drying may be performed under ambient pressure at 150 to 200° C.

(Step of Crushing Block)

When the step of crushing a block is performed, the aerogel composite block obtained by drying is crushed to obtain an aerogel composite powder. This can be achieved by placing the aerogel composite block in a jet mill, a roller mill, a bead mill, a hammer mill, or the like, and operating the mill with a moderate rotational frequency for a moderate duration.

The aerogel composite powder obtained through the above steps can be applied for a wide variety of uses with utilization of its thermal insulation and flexibility. Examples of a method for improving the thermal insulation performance of an object include a method of dispersing the powder in a liquid medium and spraying the dispersion onto an object; a method of spraying the powder onto an object having a tacky surface; a method of mixing the powder with resin or the like and applying the mixture onto an object; a method of filling voids possessed by an object with the powder; and a method of kneading the powder with resin or the like as a raw material of an object to obtain an extrudate.

EXAMPLES

Now, the present disclosure will be described in more detail with reference to the following Examples; however, these Examples are not intended to limit the present disclosure.

Example 1 [Aerogel Composite Powder]

Mixed together were 60.0 parts by mass of methyltrimethoxysilane, LS-530 (produced by Shin-Etsu Chemical Co., Ltd., product name: hereinafter, abbreviated as “MTMS”), and 40.0 parts by mass of dimethyldimethoxysilane, LS-520 (produced by Shin-Etsu Chemical Co., Ltd., product name: hereinafter, abbreviated as “DMDMS”), as silicon compounds, and 100.0 parts by mass of PL-2L (details on PL-2L are shown in Table 1, and the same is hereinafter applied for silica particle-containing raw materials), 40.0 parts by mass of water, and 80.0 parts by mass of methanol, and thereto 0.10 parts by mass of acetic acid as an acid catalyst was added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 1. To the sol 1 obtained, 40.0 parts by mass of aqueous ammonia with a concentration of 5% by mass as a base catalyst was added, and the sol 1 was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 1.

Thereafter, the wet gel 1 obtained was transferred into a plastic bottle and the plastic bottle was sealed, and thereafter the wet gel 1 was crushed by using an Extreme Mill (produced by AS ONE Corporation, MX-1000XTS) at 27000 rpm for 10 minutes to afford a particulate wet gel 1. The particulate wet gel 1 obtained was soaked in 2500.0 parts by mass of methanol, and washed at 25° C. over 24 hours. This washing operation was performed three times in total, where methanol was replaced with another one in each washing. Subsequently, the particulate wet gel washed was soaked in 2500.0 parts by mass of heptane as a solvent with low surface tension, and subjected to solvent displacement at 25° C. over 24 hours. This solvent displacement operation was performed three times in total, where heptane was replaced with another one in each solvent displacement. The particulate wet gel washed and subjected to solvent displacement was dried under ambient pressure at 40° C. for 96 hours, and thereafter further dried at 150° C. for 2 hours. Finally, the particulate wet gel was sieved (produced by TOKYO SCREEN CO., LTD., mesh size: 45 μm, wire diameter: 32 μm) to afford an aerogel composite powder 1 having the structures represented by the above formulas (4) and (5).

[Aerogel Composite Block]

The wet gel 1 obtained above was soaked in 2500.0 parts by mass of methanol, and washed at 60° C. over 12 hours. This washing operation was performed three times, where methanol was replaced with another one in each washing. Subsequently, the wet gel washed was soaked in 2500.0 parts by mass of heptane as a solvent with low surface tension, and subjected to solvent displacement at 60° C. over 12 hours. This solvent displacement operation was performed three times, where heptane was replaced with another one in each solvent displacement. The wet gel washed and subjected to solvent displacement was dried under ambient pressure at 40° C. for 96 hours, and thereafter further dried at 150° C. for 2 hours to afford an aerogel composite block 1 having the structures represented by the above formulas (4) and (5).

Example 2

Mixed together were 60.0 parts by mass of MTMS and 40.0 parts by mass of bis(trimethoxysilyl)hexane, “KBM-3066” (produced by Shin-Etsu Chemical Co., Ltd., product name), as silicon compounds, and 57.0 parts by mass of ST-OZL-35 as a silica particle-containing raw material, 83.0 parts by mass of water, and 80.0 parts by mass of methanol, and thereto 0.10 parts by mass of acetic acid as an acid catalyst and 20.0 parts by mass of cetyltrimethylammonium bromide (produced by Wako Pure Chemical Industries, Ltd.: hereinafter, abbreviated as “CTAB”) as a cationic surfactant were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 2. To the sol 2 obtained, 40.0 parts by mass of aqueous ammonia with a concentration of 5% as a base catalyst was added, and the sol 2 was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 2. Thereafter, by using the wet gel 2 obtained, an aerogel composite powder 2 and an aerogel composite block 2 each having the structures represented by the above formulas (4) and (6) were obtained in the same manner as in Example 1.

Example 3

Mixed together were 100.0 parts by mass of PL-2L as a silica particle-containing raw material, 100.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 70.0 parts by mass of MTMS and 30.0 parts by mass of DMDMS as silicon compounds were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 3. The sol 3 obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 3. Thereafter, by using the wet gel 3 obtained, an aerogel composite powder 3 and an aerogel composite block 3 each having the structures represented by the above formulas (4) and (5) were obtained in the same manner as in Example 1.

Example 4

Mixed together were 200.0 parts by mass of ST-OXS as a silica particle-containing raw material, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMS and 40.0 parts by mass of DMDMS as silicon compounds were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 4. The sol 4 obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 4. Thereafter, by using the wet gel 4 obtained, an aerogel composite powder 4 and an aerogel composite block 4 having the structures represented by the above formulas (4) and (5) were obtained in the same manner as in Example 1.

Example 5

Mixed together were 100.0 parts by mass of PL-2L-D as a silica particle-containing raw material, 100.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMS and 40.0 parts by mass of DMDMS as silicon compounds, and the resultant was reacted at 25° C. for 2 hours to afford a sol 5. The sol 5 obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 5. Thereafter, by using the wet gel 5 obtained, an aerogel composite powder 5 and an aerogel composite block 5 each having the structures represented by the above formulas (4) and (5) were obtained in the same manner as in Example 1.

Example 6

Mixed together were 87.0 parts by mass of PL-7 as a silica particle-containing raw material, 113.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMS and 40.0 parts by mass of DMDMS as silicon compounds were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 6. The sol 6 obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 6. Thereafter, by using the wet gel 6 obtained, an aerogel composite powder 6 and an aerogel composite block 6 having the structures represented by the above formulas (4) and (5) were obtained in the same manner as in Example 1.

Example 7

Mixed together were 167.0 parts by mass of PL-1 as a silica particle-containing raw material, 33.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMS and 40.0 parts by mass of DMDMS as silicon compounds were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 7. The sol 7 obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 7. Thereafter, by using the wet gel 7 obtained, an aerogel composite powder 7 and an aerogel composite block 7 each having the structures represented by the above formulas (4) and (5) were obtained in the same manner as in Example 1.

Example 8

Mixed together were 100.0 parts by mass of ST-OYL as a silica particle-containing raw material, 100.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of a block copolymer of polyoxyethylene and polyoxypropylene, F-127 (produced by BASF SE, product name), as a nonionic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 80.0 parts by mass of MTMS as a silicon compound and 20.0 parts by mass of X-22-160AS as a polysiloxane compound having the structure represented by the above formula (A) were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 8. The sol 8 obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 8. Thereafter, by using the wet gel 8 obtained, an aerogel composite powder 8 and an aerogel composite block 8 each having the structures represented by the above formulas (1) and (4) were obtained in the same manner as in Example 1.

Example 9

Mixed together were 200.0 parts by mass of PL-06L as a silica particle-containing raw material, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 80.0 parts by mass of MTMS as a silicon compound and 20.0 parts by mass of an alkoxy-modified polysiloxane compound with bifunctionality at each end having the structure represented by the above formula (B) (hereinafter, referred to as “polysiloxane compound A”) as a polysiloxane compound were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 9. The sol 9 obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 9. Thereafter, by using the wet gel 9 obtained, an aerogel composite powder 9 and an aerogel composite block 9 each having the structures represented by the above formulas (3) and (4) were obtained in the same manner as in Example 1.

The above “polysiloxane compound A” had been synthesized as follows. First, 100.0 parts by mass of dimethylpolysiloxane with a silanol group at both ends, XC96-723 (produced by Momentive Performance Materials Inc., product name), 181.3 parts by mass of methyltrimethoxysilane, and 0.50 parts by mass of t-butylamine were mixed together in a 1 L three-necked flask equipped with a stirrer, a thermometer, and a Dimroth condenser, and reacted at 30° C. for 5 hours. Thereafter, the reaction solution was heated under a reduced pressure of 1.3 kPa at 140° C. for 2 hours for removal of volatile components to afford the alkoxy-modified polysiloxane compound with bifunctionality at each end (polysiloxane compound A).

Example 10

Mixed together were 100.0 parts by mass of PL-2L as a silica particle-containing raw material, 100.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMS and 20.0 parts by mass of DMDMS as silicon compounds, and 20.0 parts by mass of the polysiloxane compound A as a polysiloxane compound were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 10. The sol 10 obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 10. Thereafter, by using the wet gel 10 obtained, an aerogel composite powder 10 and an aerogel composite block 10 each having the structures represented by the above formulas (3), (4), and (5) were obtained in the same manner as in Example 1.

Example 11

Mixed together were 143.0 parts by mass of ST-OZL-35 as a silica particle-containing raw material, 57.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMS and 20.0 parts by mass of DMDMS as silicon compounds, and 20.0 parts by mass of an alkoxy-modified polysiloxane compound with trifunctionality at each end and having the structure represented by the above formula (B) (hereinafter, referred to as “polysiloxane compound B”) as a polysiloxane compound were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 11. The sol 11 obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 11. Thereafter, by using the wet gel 11 obtained, an aerogel composite powder 11 and an aerogel composite block 11 having the structures represented by the above formulas (2), (4), and (5) were obtained in the same manner as in Example 1.

The above “polysiloxane compound B” had been synthesized as follows. First, 100.0 parts by mass of XC96-723, 202.6 parts by mass of tetramethoxysilane, and 0.50 parts by mass of t-butylamine were mixed together in a 1 L three-necked flask equipped with a stirrer, a thermometer, and a Dimroth condenser, and reacted at 30° C. for 5 hours. Thereafter, the reaction solution was heated under a reduced pressure of 1.3 kPa at 140° C. for 2 hours for removal of volatile components to afford the alkoxy-modified polysiloxane compound with trifunctionality at each end (polysiloxane compound B).

Example 12

Mixed together were 100.0 parts by mass of PL-2L and 50.0 parts by mass of ST-OZL-35 as silica particle-containing raw materials, 50.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMS and 20.0 parts by mass of DMDMS as silicon compounds and 20.0 parts by mass of the polysiloxane compound A as a polysiloxane compound were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 12. The sol 12 obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 12. Thereafter, by using the wet gel 12 obtained, an aerogel composite powder 12 and an aerogel composite block 12 having the structures represented by the above formulas (3), (4) and (5) were obtained in the same manner as in Example 1.

Comparative Example 1 [Wet Gel, Aerogel]

Mixed together were 200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 100.0 parts by mass of MTMS as a silicon compound was added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 1C. The sol 1C obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 1C. Thereafter, by using the wet gel 1C obtained, an aerogel powder 1C and an aerogel block 1C were obtained in the same manner as in Example 1.

Comparative Example 2

Mixed together were 200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 80.0 parts by mass of MTMS and 20.0 parts by mass of DMDMS as silicon compounds were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 2C. The sol 2C obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 2C. Thereafter, by using the wet gel 2C obtained, an aerogel powder 2C and an aerogel block 2C were obtained in the same manner as in Example 1.

Comparative Example 3

Mixed together were 200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 70.0 parts by mass of MTMS and 30.0 parts by mass of DMDMS as silicon compounds were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 3C. The sol 3C obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 3C. Thereafter, by using the wet gel 3C obtained, an aerogel powder 3C and an aerogel block 3C were obtained in the same manner as in Example 1.

Comparative Example 4

Mixed together were 200.0 parts by mass of water, 0.10 parts by mass of acetic acid as an acid catalyst, 20.0 parts by mass of CTAB as a cationic surfactant, and 120.0 parts by mass of urea as a thermally-hydrolyzable compound, and thereto 60.0 parts by mass of MTMS and 40.0 parts by mass of DMDMS as silicon compounds were added, and the resultant was reacted at 25° C. for 2 hours to afford a sol 4C. The sol 4C obtained was gelled at 60° C., and then aged at 80° C. for 24 hours to afford a wet gel 4C. Thereafter, by using the wet gel 4C obtained, an aerogel powder 4C and an aerogel block 4C were obtained in the same manner as in Example 1.

The modes of the silica particle-containing raw material in Examples are summarized in Table 1. The types and amounts of the Si raw materials (silicon compound and polysiloxane compound) added, and the amounts of the silica particle-containing raw material added are summarized in Table 2.

TABLE 1 Silica particle-containing raw material Silica particle Average Solid primary content particle [% by Item Name Supplier Type Shape diameter [nm] weight] Example 1 PL-2L FUSO CHEMICAL colloidal sphere 20 20 CO., LTD. silica Example 2 ST-OZL-35 Nissan Chemical colloidal sphere 100 35 Industries, Ltd. silica Example 3 PL-2L FUSO CHEMICAL colloidal sphere 20 20 CO., LTD. silica Example 4 ST-OXS Nissan Chemical colloidal sphere 5 10 Industries, Ltd. silica Example 5 PL-2L-D FUSO colloidal sphere 20 20 CHEMICAL silica CO., LTD. Example 6 PL-7 FUSO CHEMICAL colloidal cocoon 75 23 CO., LTD. silica Example 7 PL-1 FUSO CHEMICAL colloidal association 15 12 CO., LTD. silica Example 8 ST-OYL Nissan Chemical colloidal sphere 70 20 Industries, Ltd. silica Example 9 PL-06L FUSO CHEMICAL colloidal sphere 7 6 CO., LTD. silica Example 10 PL-2L FUSO CHEMICAL colloidal sphere 20 20 CO., LTD. silica Example 11 ST-OZL-35 Nissan Chemical colloidal sphere 100 35 Industries, Ltd. silica Example 12 PL-2L FUSO CHEMICAL colloidal sphere 20 20 CO., LTD. silica ST-OZL-35 Nissan Chemical colloidal sphere 100 35 Industries, Ltd. silica

TABLE 2 Silica particle-containing Si raw material raw material Amount added Amount added [part by [part by Item Type mass] mass] Example 1 MTMS 60.0 100 DMDMS 40.0 Example 2 MTMS 60.0 57 bis(trimethoxy- 40.0 silyl)hexane Example 3 MTMS 70.0 100 DMDMS 30.0 Example 4 MTMS 60.0 200 DMDMS 40.0 Example 5 MTMS 60.0 100 DMDMS 40.0 Example 6 MTMS 60.0 87 DMDMS 40.0 Example 7 MTMS 60.0 167 DMDMS 40.0 Example 8 MTMS 80.0 100 X-22-160AS 20.0 Example 9 MTMS 80.0 200 polysiloxane 20.0 compound A Example 10 MTMS 60.0 100 DMDMS 20.0 polysiloxane 20.0 compound A Example 11 MTMS 60.0 143 DMDMS 20.0 polysiloxane 20.0 compound B Example 12 MTMS 60.0 100 (PL-2L) DMDMS 20.0 50 (ST-OZL-35) poly siloxane 20.0 compound A Comparative MTMS 100.0 — Example 1 Comparative MTMS 80.0 — Example 2 DMDMS 20.0 Comparative MTMS 70.0 — Example 3 DMDMS 30.0 Comparative MTMS 60.0 — Example 4 DMDMS 40.0

[Evaluations]

Measurement or evaluation was conducted for the wet gels, aerogel composite powders, and aerogel composite blocks obtained in Examples, and the wet gels, aerogel powders, and aerogel blocks obtained in Comparative Examples, under the following conditions. Evaluation results for the gelling time in the step of forming a wet gel, the state of an aerogel composite block or aerogel block in ambient pressure drying of methanol-displaced gel, and the thermal conductivity, compression modulus, density, porosity, and average particle diameter D50 of an aerogel composite powder or aerogel powder are summarized in Table 3.

(1) Measurement of Gelling Time

Into a 100 mL airtight PP container, 30 mL of the sol obtained in each of Examples and Comparative Examples was transferred, which was used as a measurement sample. Subsequently, the measurement sample was placed in the thermostatic dryer “DVS402” (produced by Yamato Scientific Co., Ltd., product name) set at 60° C., and the time from the entrance to gelling was measured.

(2) State of Aerogel Composite Block or Aerogel Block in Ambient Pressure Drying of Methanol-Displaced Gel

In 150.0 parts by mass of methanol, 30.0 parts by mass of the wet gel obtained in each of Examples and Comparative Examples was soaked, and washed at 60° C. over 12 hours. This washing operation was performed three times, where methanol was replaced with another one in each washing. Subsequently, the wet gel washed was processed into a piece in a size of 100×100×100 mm³ by using a blade with a blade angle of approximately 20 to 25 degrees, and the piece was used as a measurement sample before drying. By using the thermostat with a safety vent “SPH (H)-202” (produced by ESPEC CORP., product name), the measurement sample before drying obtained was dried at 60° C. for 2 hours and at 100° C. for 3 hours, and then further dried at 150° C. for 2 hours to afford a measurement sample after drying (the solvent evaporation rate and so on were not controlled in any way). Then, the volume shrinkage of the sample before and after drying, SV, was determined by using the following equation. A case that the volume shrinkage, SV, was 5% or lower was rated as “not shrunk”, and a case that the volume shrinkage, SV, was 5% or higher was rated as “shrunk”.

SV=(V ₀ −V ₁)/V ₀×100

In the equation, V₀ denotes the volume of a sample before drying; and V₁ denotes the volume of the sample after drying.

(3) Measurement of Average Particle Diameter, D50

An aerogel composite powder or aerogel powder was added to ethanol to a concentration of 0.5% by mass, and the resultant was vibrated with a 50 W ultrasonic homogenizer for 20 minutes. Thereafter, 10 mL of the dispersion was injected into a Microtrac MT3000 (produced by Nikkiso Co., Ltd., product name), and the particle diameter was measured at 25° C. with a refractive index of 1.3 and absorption of 0. And then, a particle diameter at 50% of the cumulative value (volume-based) in the particle size distribution was used as the average particle diameter, D50.

(4) Measurement of Thermal Conductivity

An aerogel composite block or aerogel block was processed into a piece in a size of 150×150×100 mm³ by using a blade with a blade angle of approximately 20 to 25 degrees, and the piece was used as a measurement sample. Subsequently, the measurement sample was shaped with a sand paper of #1500 or finer to thoroughly smooth the surface, as necessary. Before measurement of thermal conductivity, the measurement sample obtained was dried by using the thermostatic dryer “DVS402” (produced by Yamato Scientific Co., Ltd., product name) under the atmospheric pressure at 100° C. for 30 minutes. The measurement sample was then transferred into a desiccator and cooled to 25° C. Thus, a measurement sample for measurement of the thermal conductivity was obtained.

Measurement of thermal conductivity was conducted by using the thermal conductivity analyzer based on a steady state method “HFM 436 Lambda” (produced by NETZSCH, product name). Measurement conditions were set such that measurement was performed under the atmospheric pressure at an average temperature of 25° C. The measurement sample obtained as described above was sandwiched between an upper heater and a lower heater with a load of 0.3 MPa, the temperature difference, ΔT, was set to 20° C., and the upper surface temperature, lower surface temperature, and so on of the measurement sample were measured while the heat flow was adjusted to a one-dimensional heat flow by using a guard heater. The thermal resistance, R_(S), of the measurement sample was determined by using the following equation:

R _(S) =N((T _(U) −T _(L))/Q)−R _(O)

wherein T_(U) denotes the upper surface temperature of the measurement sample; T_(L) denotes the lower surface temperature of the measurement sample; R_(O) denotes the contact thermal resistance of the upper/lower interface; and Q denotes output from a heat flux meter. N denotes a proportionality coefficient, and had been determined in advance by using a calibration sample.

From the thermal resistance, R_(S), obtained, the thermal conductivity, λ, of the measurement sample was determined by using the following equation:

λ=d/R _(S)

wherein d denotes the thickness of the measurement sample.

(5) Measurement of Compression Modulus

An aerogel composite block or aerogel block was processed into a cube (dice) of 7.0×7.0×7 0 mm by using a blade with a blade angle of approximately 20 to 25 degrees, and the cube was used as a measurement sample. Subsequently, the measurement sample was shaped with a sand paper of #1500 or finer to thoroughly smooth the surface, as necessary. Before measurement, the measurement sample obtained was dried by using the thermostatic dryer “DVS402” (produced by Yamato Scientific Co., Ltd., product name) under the atmospheric pressure at 100° C. for 30 minutes. The measurement sample was then transferred into a desiccator and cooled to 25° C. Thus, a measurement sample for measurement of the compression modulus was obtained.

For the measurement apparatus, the compact table-top tester “EZ Test” (produced by Shimadzu Corporation, product name) was used. A load cell of 500 N was used. An upper platen (ϕ20 mm) and lower platen (ϕ118 mm) each made of stainless steel were used as jigs for compression measurement. The measurement sample was set between the upper platen and lower platen positioned in parallel, and compressed at a speed of 1 mm/min. The measurement temperature was 25° C., and the measurement was terminated at a point of time when a load of higher than 500 N was applied or when the measurement sample was broken. Here, the strain, ε, was determined by using the following equation:

ε=Δd/d1

wherein Δd denotes the change in thickness (mm) of the measurement sample caused by a load; and d1 denotes the thickness (mm) of the measurement sample before application of a load.

The compressive stress (MPa), σ, was determined by using the following equation:

σ=F/A

wherein F denotes compressive force (N); and A denotes the cross-sectional area (mm²) of the measurement sample before application of a load.

The compression modulus (MPa), E, was determined in a range of compressive force from 0.1 to 0.2 N by using the following equation:

E=(σ₂−σ₁)/(ε₂−ε₁)

wherein σ₁ denotes compressive stress (MPa) measured at a compressive force of 0.1 N; σ₂ denotes compressive stress (MPa) measured at a compressive force of 0.2 N; ε₁ denotes compressive strain measured at a compressive stress of σ₁; and ε₂ denotes compressive strain measured at a compressive stress of σ₂.

(6) Measurement of Density and Porosity

The density and porosity of an aerogel composite block or aerogel block, with regard to the pore (through-hole) connected as a three-dimensional network, were measured by using mercury porosimetry in accordance with DIN 66133. The measurement temperature was room temperature (25° C.), and an AutoPore IV9520 (produced by Shimadzu Corporation, product name) was used for the measurement apparatus.

TABLE 3 Wet gel Aerogel composite (aerogel) State of gel after Block Gelling ambient pressure Powder Thermal Compressive time drying of methanol- D50 conductivity modulus Density Porosity Item [min] displaced gel [μm] [W/(m · K)] [MPa] [g/cm³] [%] Example 1 30 not shrunk 24 0.030 0.44 0.19 85.3 Example 2 60 not shrunk 32 0.022 0.98 0.18 89.2 Example 3 30 not shrunk 18 0.027 1.37 0.19 86.1 Example 4 60 not shrunk 25 0.030 0.43 0.19 86.7 Example 5 60 not shrunk 23 0.030 0.51 0.19 86.5 Example 6 30 not shrunk 26 0.028 0.55 0.19 86.2 Example 7 30 not shrunk 23 0.030 0.42 0.19 86.4 Example 8 60 not shrunk 21 0.018 1.47 0.18 90.6 Example 9 60 not shrunk 19 0.018 1.68 0.18 91.2 Example 10 30 not shrunk 20 0.023 0.94 0.18 89.3 Example 11 60 not shrunk 27 0.018 1.39 0.19 90.1 Example 12 30 not shrunk 25 0.022 1.08 0.19 89.6 Comparative 180 shrunk 12 0.017 7.40 0.17 91.2 Example 1 (with crack) Comparative 180 shrunk 15 0.028 4.35 0.18 90.8 Example 2 (with crack) Comparative 210 shrunk 20 0.041 1.25 0.18 86.8 Example 3 (with crack) Comparative 240 not shrunk 36 0.045 0.15 0.19 86.4 Example 4

Table 3 shows that each of the aerogel composite powders and blocks in Examples had a short gelling time in the step of forming a wet gel and was excellent in reactivity, and had good shrinkage resistance in ambient pressure drying of methanol-displaced gel. In addition, it is understood that each of the aerogel composite blocks in Examples has a low thermal conductivity and low compression modulus, and the corresponding aerogel composite powder with the same composition is also superior in both thermal insulation and flexibility.

In each of Comparative Examples 1 to 3, in contrast, the gelling time in the step of forming a wet gel was long, and the gel shrunk and a crack was generated in the surface in ambient pressure drying of methanol-displaced gel. In addition, one of thermal conductivity and flexibility was poor. In Comparative Example 4, the shrinkage resistance and flexibility were sufficient, but the gelling time was long and the thermal conductivity was high.

REFERENCE SIGNS LIST

-   -   1 . . . aerogel particle     -   2 . . . silica particle     -   3 . . . pore     -   10 . . . aerogel composite     -   L . . . circumscribed rectangle 

1. An aerogel composite powder comprising: an aerogel component; and a silica particle.
 2. The aerogel composite powder according to claim 1, having: a three-dimensional network skeleton formed of the aerogel component and the silica particle; and a pore.
 3. An aerogel composite powder comprising a silica particle as a component constituting a three-dimensional network skeleton.
 4. An aerogel composite powder as a dried product of a wet gel, wherein the wet gel is a condensate of a sol comprising: a silica particle; and at least one selected from the group consisting of a silicon compound having a hydrolyzable functional group or a condensable functional group and a hydrolysis product of the silicon compound having a hydrolyzable functional group.
 5. The aerogel composite powder according to claim 1, as a dried product of a wet gel, wherein the wet gel is a condensate of a sol comprising: a silica particle; and at least one selected from the group consisting of a silicon compound having a hydrolyzable functional group or a condensable functional group and a hydrolysis product of the silicon compound having a hydrolyzable functional group.
 6. The aerogel composite powder according to claim 4, wherein the silicon compound further comprises a polysiloxane compound having a hydrolysable functional group or a condensable functional group.
 7. The aerogel composite powder according to claim 6, wherein the polysiloxane compound includes a compound having a structure represented by the following formula (B):

wherein R^(1b) represents an alkyl group, an alkoxy group, or an aryl group; R^(2b) and R^(3b) each independently represent an alkoxy group; R^(4b) and R^(5b) each independently represent an alkyl group or an aryl group; and m represents an integer of 1 to
 50. 8. The aerogel composite powder according to claim 1, having a ladder-type structure including struts and a bridge, wherein the bridge has a structure represented by the following formula (2):

wherein R⁵ and R⁶ each independently represent an alkyl group or an aryl group; and b represents an integer of 1 to
 50. 9. The aerogel composite powder according to claim 8, having a ladder-type structure represented by the following formula (3):

wherein R⁵, R⁶, R⁷, and R⁸ each independently represent an alkyl group or an aryl group; a and c each independently represent an integer of 1 to 3000; and b represents an integer of 1 to
 50. 10. The aerogel composite powder according to claim 1, wherein an average primary particle diameter of the silica particle is 1 to 500 nm.
 11. The aerogel composite powder according to claim 1, wherein a shape of the silica particle is spherical.
 12. The aerogel composite powder according to any claim 1, wherein the silica particle is an amorphous silica particle.
 13. The aerogel composite powder according to claim 12, wherein the amorphous silica particle is at least one selected from the group consisting of a fused silica particle, a fumed silica particle, and a colloidal silica particle.
 14. The aerogel composite powder according to claim 1, wherein an average particle diameter D50 is 1 to 1000 μm. 